The invention relates generally to the commercial and industrial refrigeration art, and more particularly to surge receiver and gas defrost systems and high side pressure controls for such systems.
In the past, closed refrigeration systems having a single compressor or plural compressors have been used in commercial installations, such as supermarkets having a large number of different low and/or normal temperature refrigerated fixtures or units for the display and storage of products, or for industrial installations such as warehousing, lockers, manufacturing plants and the like having varying refrigeration requirements. Hot gas defrosting in such systems is well-known and effective due to the large latent heat load extracted from such products in the refrigerated units in excess of the heat required for defrosting one or more selected evaporator coils during the continued refrigeration of the remaining fixtures. However, highly superheated hot gas taken directly from the compressor discharge for defrosting selected evaporators has resulted in several adverse conditions, including breakage and leaks caused by the rapid thermal expansion and contraction of refrigerant lines and other components, and the fog or steam caused by the excessive defrost temperatures frequently is visual in the refrigerated fixture or zone and often results in the buildup of frost on the products.
U.S. Pat. No. 3,343,375 teaches that the adverse effects of prior hot gas defrosting can be obviated by using refrigerant gas at substantially saturation temperature as when taken from the receiver or otherwise desuperheated, and some benefits of surge receiver systems employing so-called saturated gas defrost are disclosed in U.S. Pat. Nos. 3,358,469 and 3,427,819, which also show high side head pressure and equalizer controls. However, although the advantages and benefits of using these separate features are recognized in these and other prior art patents, none of these prior systems has successfully utilized saturated gas defrost in combination with surge receiver systems or provided functional high side controls that make such a combination practical and economically sound. It is recognized that refrigeration system operations throughout the year are directly affected by various climatic conditions. For instance, during winter operations the maintenance of proper compressor head pressures in the high side of the system has been a principal problem, particularly in recent years in which heat reclamation condensers have come into wide-spread usage; and during summer operations in which the machine room temperature was frequently below the condensing temperature of a roof-mounted or outside condenser, the supply of saturated gas for defrosting was severely limited or substantially non-existent due to its condensation to liquid form and overfilling of the receiver.
In short, prior systems having surge receivers and utilizing saturated gas defrost and winter heat reclamation condensers have had various high side control problems in the various climatic seasons adversely affecting such systems and, while various control arrangements have been proposed, year-round system operations have not been efficient or adequately controlled heretofore.